The invention relates to a turning and quality assurance process for thermally sprayed, rotationally symmetrical grazing and running-in linings of turbomachines.
Thermally sprayed linings are used in turbomachines, in particular in gas turbines, as porous grazing or running-in linings. On the one hand, they are not to be too soft (porous) in order to resist the high loads caused by alternating gas forces and vibrations; on the other hand, they must be soft enough in order not to damage the grazing or running-in partner, e.g. a blade tip or a sealing lip (sealing fin). The hardness of the linings is set by varying the spraying parameters. However, they can only be measured in a very inadequate manner by a special ball impression method. The results have considerable spread and are no reliable measure of the quality of the coating. In addition, they depend on the geometry.
In many cases, the hardness is also measured on reference specimens which have been sprayed with the same parameter setting. Transferring the values thus determined to the component is likewise problematical.
After the spraying, the linings have excess material, which is removed again during the finish machining. The top coating, that is to say the coating finally applied during the spraying, generally has a different, harder consistency than the rest of the lining material. This is also to be taken into account during testing.
The substantial disadvantages of the known processes therefore consist in the fact that measurements can often only be taken on specimens and not on the component itself and also in the fact that the quality test as such—even on the component—delivers relatively unreliable results.
DE 197 30 008 C1 (corresponding U.S. Pat. No. 6,177,174) protects armor plating for a metallic engine component and a process of producing it. Such components are in particular sealing tips of labyrinth seals or blade tips which interact with corresponding grazing or running-in linings. An embodiment of this patent provides for the component to be finish-machined by turning after the coating with a ceramic material, preferably by means of thermal spraying.
DE 42 28 333 A1 (corresponding U.S. Pat. No. 5,506,786) relates to a metal-cutting apparatus for finish machining a surface of a workpiece of a metallic material, having a detection device for the cutting force exerted on the metal-cutting apparatus by the workpiece. The apparatus is preferably used for the superfine finish turning of photoreceptor cells, the requirements for the surface quality being extremely high. Typical features of such an apparatus are a monocrystalline diamond tool, a feed device for a liquid cutting lubricant and a disposal device for chips. Before the actual series production, test series with varying machining parameters are run and the cutting force characteristic is measured and stored in each case. Typical cutting force characteristics are obtained in the event of machining errors, such as vibrations, scratches, chip accumulation, unmachined material, etc. In series production, the cutting force characteristic for each component is measured, stored and compared with the characteristic from the test series. If there is a large degree of correspondence with a typical “error characteristic” (e.g. vibrations), this is an indication that the respective component is likewise defective. If need be, the machining parameters then have to be changed. The metal-cutting apparatus described and the associated processes are thus only suitable for the precision machining of surfaces.
Against this background, the object of the invention is to specify a turning and quality assurance process for thermally sprayed, rotationally symmetrical grazing and running-in linings of turbomachines which detects the lining quality on the component itself, which advantageously combines the quality test with the machining and which delivers reliable, reproducible measured values for the entire effective lining region.
This object is achieved by removing a top coating, which is harder in relation to a nominal lining consistency, finish-turning to size the lining still having excess material, maintaining turning parameters defined during the finish-turning, detecting the cutting force or a force proportional thereto quantitatively in a characteristic, recording graphically or storing in a data system said characteristic, comparing the force characteristic with predetermined limit values, and, depending on a result of the comparing, approving the lining for use or removing again and producing again with altered spraying parameters.
The turning itself is carried out in two steps, the first serving for the material removal of the relatively hard top layer, the second serving for the actual machining to size. During the second step (finish turning), defined turning parameters (cutting speed, feed, recessing depth, etc.) are maintained and the cutting force characteristic is quantitatively detected and is recorded graphically or in a data system. The force characteristic is compared with predetermined limit values, in which case, as a result, the lining is approved for use or is removed and produced again. For the definition of the decisive limit values, it will be necessary to produce actual linings while varying the spraying parameters, to detect the cutting force characteristic during the turning and to store it, and to test the grazing or running-in behavior of the lining variants. In the process, good to useful and less useful to useless variants will be obtained, the cutting force characteristics of which lead to the desired limit values.
Preferred developments of the process according to the main claim are characterized in the subclaims.
The invention is explained in more detail below with reference to the figures.